Pipettes are hand-held liquid dispensing devices that are used for delivering a precisely defined amount of liquid from one receptacle to another receptacle. Liquid is aspirated into and delivered from a disposable tip that is attached to a lower end of the pipette.
In air displacement pipettes, downward thumb action on a control knob moves a plunger downward within a cylinder from an upper stop against the upward bias of a return spring to a lower stop, whereby air is displaced from the cylinder. To aspirate a desired volume of liquid into the tip, the user places an end of the tip in a sample liquid and releases the control knob to allow the return spring to return the plunger to the upper stop. Finally, to dispense the desired volume of liquid, the user moves the tip of the pipette to a receptacle for receiving the liquid and presses the control knob with his thumb to move the plunger from the upper stop to the lower stop. The amount of liquid aspirated and dispensed corresponds to the volume of displaced air.
A pipette typically has a mechanism for the removal of the tip so that the user does not need to pull off the tip by grasping it manually. The tip is held in place at the lower end of a pipette's tip cone by friction. To detach the tip, the user presses a tip removal button that is operable by the user's thumb and typically located in the upper part of the pipette, near the control knob that is used for aspirating and dispensing. The mechanism comprises a removal sleeve sliding on a cylinder part of the pipette and an arm fixed thereto and sliding in the handle of the pipette or on its side. The mechanism is connected with a spring, which pushes the arm into the upper position. When the arm is pressed downwards, the sleeve disengages the tip attached to the tip cone, i.e. the end of the cylinder.
Different solutions for realising the tip removal mechanism are known in the prior art:
U.S. Pat. No. 5,435,197 describes a tip remover that is based on a lever mechanism. The lever projects sideways from the frame of the pipette, and the arm of the tip remover is articulated between the ends of the lever. The end on the side of the frame of the lever is best formed into a gear, which is in mesh with a toothing in the direction of the arm in the pipette frame.
US 2003/0147781 A1 describes a pipette comprising a body; an arm movable relative to the body parallel to a longitudinal direction of the pipette in order to eject a cone fixed to the body; and a button for controlling movement of the arm. The pipette is arranged in such a manner that the button applies sliding thrust on the arm while the arm is moving relative to the body.
US 2007/0272037 A1 describes a tip removing mechanism that comprises a rotatable ramp member, having a circle-forming ramp surface with one or more segments, each of said segments having a top position and a bottom position on the ramp surface. In a basic condition, the remover element is in the top position. In response to its rotation, the ramp member forces the remover element towards the tip. A segment is followed by stopping the ramp member at the commencement of a next segment and a new tip can be attached to the pipette. The mechanism can be provided with a spring for returning the remover element. The ramp member can be rotated by means of a motor, such as an electric motor. Stopping of the motor after a segment is most preferably performed automatically. Here the removal function of the tip is effected by means of a one-way rotating action.
The above described known tip removal mechanisms are based on a sleeve mechanism in which the tip is subjected to a downward directed force submitted by the sleeve. The force is generated by the user's finger to overcome the friction between the tip and the tip cone. Once the required force is reached, the tip will fall off and become detached, and the sleeve will continue to move in an accelerated manner to its lower stop. The result is an abrupt removal of the tip with a high speed, since the user is not able to fully control the removal speed. When removing a tip, the user typically needs to direct the tip towards a container that is preferably located farther away, as it is not desirable to shoot the tip with a high speed against a nearby desk surface or a container. A major disadvantage of the known removal mechanisms is the spreading of aerosols upon high-speed tip removal, which results in contamination problems.
When the tip removal mechanism is based on a sleeve or a side-arm that is adapted for pushing the tip, the construction of the pipette becomes bulky and larger than what is needed for accommodating the user's hand. In addition, the required force to push the removal button is usually relatively high, which may lead to fatigue of the user's thumb. Thus, the known tip removal mechanisms are not optimal in view of ergonomics.
In addition, because the above-described ejector sleeve is a moving part, at least one seam is formed between the sleeve and the handle or body of the pipette. Such a seam is prone to collect dirt over time, which is highly undesirable.
The present invention is directed to overcome the above described disadvantages present in the known tip removal mechanisms.
The present invention provides a controlled removal that resembles gentle dropping of the tip thus avoiding spreading of aerosols. Further, the present invention improves the construction and ergonomics of the pipette and makes the pipette more robust and compact.